In order to protect sheet material in particular valuable documents it is known to hot seal the sheet material with a laminating foil. This is done in the non industrial field, this means in the office and personal field through laminating units typically configured as table top units. Such laminating units are known e.g. from DE 20 2005 005 020 U1; and in combination with a cutting unit, they are known from EP 1 724 111 A2. They have essentially the same configuration; this means a housing in which a laminating apparatus is disposed. Between a feed opening on one side and an exit opening on the other side of the housing a pass through channel extends through the housing, wherein the laminating apparatus is associated with the pass through channel. The latter typically comprises at least one pair of rollers, possibly also several pairs of rollers, made of two respective laminating rollers disposed on top of one another and forming a laminating gap, wherein the laminating gap is adjusted, so that the combination of sheet material and laminating foil in the laminating gap is exposed to substantial pressure. In hot laminating units at least one of the laminating rollers, typically both are heated, so that the combination of sheet material and laminating foil is also heated additionally. During passage the laminating foils are glued together with the sheet material to be heat-sealed there between.
Typically, the sheet material is heat-sealed in between two foil sheets forming a laminating foil. These can be loose foil sheets or foil webs which are rolled up within the laminating unit and which are pulled off from the rollers during the laminating process, wherein the separation is provided through cutting apparatuses (re. US 2004/0050500 A1). Instead, the two foil sheets can also be provided in the form of a laminating foil pouch, wherein the two foil sheets are connected with one another at least at one lateral edge. Such laminating foils are known e.g. from DE 197 44 595 A1 and DE 201 00 328 U1. The foil sheets are configured as composite foils, wherein a transparent clear foil e.g. made from polypropylene is provided with a heat resistant glue layer which is made e.g. from EVA (Ethylen-Vinylacetate-Copolymer) (Re. DE 600 29 505 T2).
For the time being, laminating foils with a thickness of 30 μm to 500 μm are commercially available. Selecting the foil thickness can provide a desired flexibility or stiffness to the laminated sheet material. It is implied that more thermal energy has to be provided for hot sealing thick laminating foils, than has to be provided for hot sealing thin laminating foils made of the same materials. Laminating units, which are configured for processing laminating foils with different thickness therefore have to be adaptable to the thickness of the respective thickness of the laminating foil to be processed, so that on the one hand sufficient thermal energy is provided for welding the sheet material, on the other hand the laminating foil does not overheat so that it is damaged. Therefore such laminating units comprise adjustment apparatuses through which the temperature of the laminating apparatus and/or the pass through velocity can be adapted to the respective thickness of the laminating foil by hand.
However, in practical applications it has become apparent that there are always operator errors, in particular when, as in large offices, many persons have access to a laminating unit. An operator error has the consequence that the lamination is insufficient for a heat impact which is too small, thus the laminated sheet material is not protected sufficiently or that the laminating foil overheats for excessive heat impact and thus sticks to the laminating rollers which causes severe damages to the laminating unit. Furthermore, the laminated sheet material is damaged, so it is unreadable. The latter condition is mostly non repairable and in the worst case causes the destruction of the document.
DE 100 04 486 A1 discloses a cartridge laminating unit in which a control and/or regulation apparatus is provide through which control elements can be controlled which influence the laminating process as a function of properties of the respective cover to be laminated, which properties are detected by a sensor, wherein the control elements are e.g. the heating apparatus for adjusting a particular laminating temperature and/or a drive apparatus for adjusting a particular laminating speed and/or a press apparatus for adjusting a particular laminating pressure. For this purpose the roll film cartridge has a machine readable encoding strip on its outer surface, e.g. a typical bar code strip. Alternatively, the encoding can also be provided directly at the roll film and can e.g. be detected through a window in the cartridge wall, or at an end of the roll film which protrudes from the output slot. It is also conceivable that the roll film cartridge or the roll film is provided with a mechanically detected marking which can be detected by a detector and which can be converted into an electrical sensor signal which can be transmitted to a control unit.